1. Field of the Invention
The invention relates to a picture display device comprising a cathode ray tube with a tube base, which cathode ray tube comprises an electron gun with a cathode and electrostatic grids which are connected to glass rods. The invention also relates to a cathode ray tube comprising an electron gun with a cathode. Moreover, the invention relates to an electron gun provided with a cathode. This type of picture display device may comprise a conventional cathode ray tube or a flat-panel cathode ray tube.
2. Description of Related Art
A cathode ray tube for a monochrome picture display device, for example a television or monitor, has a display screen with a regular pattern of phosphor elements constituting pixels. The cathode ray tube also comprises an electron gun with a cathode, which electron gun emits an electron beam during operation. This beam may be sent to a given location on the display screen by means of deflection coils which generate a given electric field. The display screen is now activated by sweeping the electron beam along it, while the beam is modulated by a video signal. This video signal ensures that the phosphor elements are excited in such a way that their luminescence produces an image. When many electrons land on the element during the period of excitation, the element lights up to a brighter extent. There are many elements per surface unit. Moreover, the elements are excited one after the other within a very short time. The viewer thus experiences a moving image at a normal viewing distance. In a color display device, for example a color television or a color monitor, each pixel comprises three phosphor elements each luminescing in a different primary color when they are excited. There are, as it were, three uniform regular patterns on the display screen, each pattern having a different color. Instead of one electron beam, three electron beams from three different cathodes in the electron gun are swept along the screen during operation. Each of these three beams excites the pixels of a given color. Since the phosphor elements of a pixel are located close together, the viewer observes them jointly rather than separately. The color which is experienced is a mixed color of the three elements. By exciting each element with a given intensity, the viewer experiences a given color. For example, when the red element and the blue element are excited to a strong extent and the green element is excited to a weak extent, the viewer will experience the mixed color of purple. Similarly as in a monochrome cathode ray tube, the pixels are located so close together that the viewer does not see them separately at a normal viewing distance. A color image is the result.
Known picture display devices have a considerable drawback. The electron gun has a too high operating temperature so that the lifetime is limited and the picture quality occurring during start-up of the picture display device is not optimal.